tcg: Sanity check goto_tb input

Checking that we don't try for idx != [01] is trivial.  Checking
that we don't issue more than one of any index requires a tad
more data and some ifdefs protecting that new variable.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
diff --git a/tcg/tcg.c b/tcg/tcg.c
index b3c2650..c069e44 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -298,6 +298,10 @@
     s->nb_labels = 0;
     s->current_frame_offset = s->frame_start;
 
+#ifdef CONFIG_DEBUG_TCG
+    s->goto_tb_issue_mask = 0;
+#endif
+
     gen_opc_ptr = gen_opc_buf;
     gen_opparam_ptr = gen_opparam_buf;
 }